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A long search eventually confirms a new species of arboreal rat, but it’s already at risk of extinction. Andrew Masterson reports.

A new species of giant rat that lives up trees and can crack open coconuts with its teeth has been discovered living in the Solomon Islands.

The rat – dubbed Uromys vika – weighs about a kilogram, which makes it five times heavier than a regular black rat (Rattus rattus).

The discovery is formally described in the Journal of Mammalogy, and for one of the co-authors, Tyrone Lavery of Chicago’s Field Museum, publication marks the end of a seven year quest to confirm the existence of the species.

When he first began hearing reports from locals of a huge unfamiliar arboreal rodent, there were already eight known wild rat species recorded in the Solomons. The locals called this one “vika”, but despite extensive searches Lavery never managed to see one, dead or alive.

“I started to question if it really was a separate species, or if people were just calling regular black rats 'vika’,” he says.

Part of the problem, he adds, was that the mysterious animal was reputed to live high in the branches.

“If you’re looking for something that lives on the ground, you’re only looking in two dimensions, left to right and forward and backward. If you're looking for something that can live in 30-foot-tall trees, then there's a whole new dimension that you need to search.”

The rat’s tree-dwelling habits added an extra urgency to the need to confirm whether or not it actually existed. Forests in the Solomon Islands are being cut down – legally and otherwise – at a voracious rate, with local parliamentarians this year describing it as “unsustainable”.

With so much land being deforested so quickly, there was a very real risk that the tree rat could be made extinct before its existence could be confirmed.

Then, last year, Lavery caught a lucky break. He saw an unfamiliar rat run out from a fallen tree, and succeeded in capturing it.

“As soon as I examined the specimen, I knew it was something different,” he says. “Looking at the features on its skull, I could rule out a bunch of species right away.”

After DNA comparisons confirmed that Lavery’s catch was indeed a previously unrecorded species, Uromys vika became the first new type of rat found on the islands for 80 years.

Its giant size and powerful jaws, Lavery suggests, are evolutionary adaptations to island life. “Vika’s ancestors probably rafted to the island on vegetation, and once they got there, they evolved into this wonderfully new species, nothing like what they came from on the mainland,” he explains.

Because of the level of logging on the Solomon Islands, the rat has already been classified as critically endangered.

“The discovery marks an important moment in the biological study of the Solomon Islands, especially since vika is so uncommon and close to extinction,” says Lavery.

“Finding a new mammal is really rare – there are probably just a few dozen new mammals discovered every year. Vika was so hard to find, and the fact that I was able to persevere is something that I'm proud of.”